The invention relates to a plastic film heat seal apparatus.
There has been commercially available a plastic bag making machine in which a heat seal bar is pressed against superposed layers of plastic film so that the layers of plastic film can be heat sealed with each other by the heat seal bar to have a heat sealed portion whenever the layers of plastic film are intermittently fed in a direction and temporarily stopped. The heat seal bar is then retreated and spaced from the layers of plastic film to permit the layers of plastic film to be fed again after being heat sealed. This arrangement is essential to successively make plastic bags. In addition, it is frequent practice in the apparatus that the heat seal bar is covered with at least one low adhesive sheet. The low adhesive sheet is interposed between the heat seal bar and the layers of plastic film for protection of the layers of plastic film when the heat seal bar is pressed against the layers of plastic film. The low adhesive sheet may be patterned with meshes so that the layers of plastic film can be heat sealed to be patterned with meshes by the low adhesive sheet. The low adhesive sheet may be a glass wool teflon (trade mark) sheet.
However, the low adhesive sheet should adhere to the layers of plastic film while the heat seal bar is pressed against the layers of plastic film. The low adhesive sheet is then pulled from and peeled off the layers of plastic film abruptly and at once all over the heat sealed portion of the layers of plastic film to generate a large noise when the heat seal bar is retreated and spaced from the layers of plastic film after the layers of plastic film are heat sealed. The heat sealed portion may therefore be damaged by the low adhesive sheet, resulting in seal defect. The layers of plastic film may be fed again while the low adhesive sheet is not peeled off but kept adhering to the layers of plastic film, resulting in snaking of the layers of plastic film. The layers of plastic film may be fed again to be elongated by the low adhesive sheet not peeled off, resulting in irregularity in fed pitch or fed length.
It is also usual in the apparatus that a cooling bar is pressed against the layers of plastic film so that the layers of plastic film can be cooled by the cooling bar after being heat sealed to have a cooled portion whenever the layers of plastic film are intermittently fed in the plastic film feeding direction and temporarily stopped, The cooling bar is then retreated and spaced from the layers of plastic film to permit the layers of plastic film to be fed again after being cooled. The cooling bar may be covered with at least one low adhesive sheet which is interposed between the cooling bar and the layers of plastic film for protection of the layers of plastic film when the cooling bar is pressed against the layers of plastic film.
However, the adhesive sheet should adhere to the layers of plastic film while the cooling bar is pressed against the layers of plastic film. The low adhesive sheet is then pulled from and peeled off the layers of plastic film abruptly and at once all over the cooled portion of the layers to generate a large noise when the cooling bar is retreated and spaced from the layers of plastic film after the layers of plastic film are cooled. This may result in seal defect, snaking of the layers of plastic film and irregularity in fed pitch or fed length, as in the case of the low adhesive sheet of the heat seal bar.
It is therefore an object of the invention to provide a new and improved plastic film heat seal apparatus to overcome the above problems.
Another object of the invention is to provide the apparatus in which the low adhesive sheet can be peeled off the layers of plastic film conveniently and smoothly.
According to the invention, there is provided a plastic film heat seal apparatus which comprises a heat seal bar covered with at least one low adhesive sheet. The heat seal bar is pressed against superposed layers of plastic film so that the layers of plastic film can be heat sealed with each other by the heat seal bar to have a heat sealed portion whenever the layers of plastic film are intermittently fed in a direction and temporarily stopped. The low adhesive sheet is interposed between the heat seal bar and the layers of plastic film for protection of the layers of plastic film when the heat seal bar is pressed against the layers of plastic film. The heat seal bar is then retreated and spaced from the layers of plastic film to permit the layers of plastic film to be fed again after being heat sealed. The heat sealed portion includes upstream and downstream edges in the plastic film feeding direction.
The apparatus further comprises loosening means by which the low adhesive sheet is loosened at a position upstream of the heat seal bar in the plastic film feeding direction after the heat seal bar is pressed against the layers of plastic film The apparatus further comprises holding means by which the low adhesive sheet is held at a position downstream of the heat seal bar in the plastic film feeding direction. The low adhesive sheet is therefore pulled by and peeled off the layers of plastic film gradually and progressively in a direction to the upstream edge from the downstream edge of the heat sealed portion when the layers of plastic film are fed again after being heat sealed.
In a preferred embodiment, the heat seal bar is positioned on the upper side of the layers of plastic film. The loosening means comprises a first member disposed at a position upstream of the heat seal bar in the plastic film feeding direction. The low adhesive sheet extends upward toward the first member to be engaged with the first member. The loosening means further comprises drive means connected to the first member. The first member is moved downward by the drive means so that the low adhesive sheet can be loosened by the first member. The holding means comprises a second member disposed at a position downstream of the heat seal bar in the plastic film feeding direction. The low adhesive sheet extends upward toward the second member to be engaged with and held by the second member.
The apparatus further comprises a rubber covered with at least one additional low adhesive sheet. The layers of plastic film are directed between the heat seal bar and the rubber. The heat seal bar is pressed against the layers of plastic film and the rubber with the additional low adhesive sheet interposed between the rubber and the layers of plastic film.
The apparatus further comprises additional loosening means by which the additional low adhesive sheet is loosened at a position upstream of the rubber in the plastic film feeding direction after the heat seal bar is pressed against the layers of plastic film and the rubber. The apparatus further comprises additional holding means by which the additional low adhesive sheet is held at a position downstream of the rubber in the plastic film feeding direction. The additional low adhesive sheet is therefore pulled by and peeled off the layers of plastic film gradually and progressively in a direction to the upstream edge from the downstream edge of the heat sealed portion when the layers of plastic film are fed again after being heat sealed.
There is also provided a plastic film heat seal apparatus which comprises a cooling bar covered with at least one low adhesive sheet. The cooling bar is pressed against superposed layers of plastic film so that the layers of plastic film can be cooled by the cooling bar after being heat sealed to have a cooled portion whenever the layers of plastic film are intermittently fed in a direction and temporarily stopped. The low adhesive sheet is interposed between the cooling bar and the layers of plastic film for protection of the layers of plastic film when the cooling bar is pressed against the layers of plastic film. The cooling bar is then retreated and spaced from the layers of plastic film to permit the layers of plastic film to be fed again after being cooled. The cooled portion includes upstream and downstream edges in the plastic film feeding direction.
The apparatus further comprises loosening means by which the low adhesive sheet is loosened at a position upstream of the cooling bar in the plastic film feeding direction after the cooling bar is pressed against the layers of plastic film. The apparatus further comprises holding means by which the low adhesive sheet is held at a position downstream of the cooling bar in the plastic film feeding direction. The low adhesive sheet is therefore pulled by and peeled off the layers of plastic film gradually and progressively in a direction to the upstream edge from the downstream edge of the cooled portion when the layers of plastic film are fed again after being cooled.
In a preferred embodiment, the cooling bar is positioned on the upper side of the layers of plastic film. The loosening means comprises a first member disposed at a position upstream of the cooling bar in the plastic film feeding direction. The low adhesive sheet extends upward toward the first member to be engaged with the first member. The loosening means further comprises drive means connected to the first member. The first member is moved downward by the drive means so that the low adhesive sheet can be loosened by the first member. The holding means comprises a second member disposed at a position downstream of the cooling bar in the plastic film feeding direction. The low adhesive sheet extends upward toward the second member to be engaged with and held by the second member.
The apparatus further comprises a rubber covered with at least one additional low adhesive sheet. The layers of plastic film is directed between the cooling bar and the rubber. The cooling bar is pressed against the layers of plastic film and the rubber with the additional low adhesive sheet interposed between the rubber and the layers of plastic film.
The apparatus further comprises additional loosening means by which the additional low adhesive sheet is loosened at a position upstream of the rubber in the plastic film feeding direction after the cooling bar is pressed against the layers of plastic film and the rubber. The apparatus further comprises additional holding means by which the additional low adhesive sheet is held at a position downstream of the rubber in the plastic film feeding direction. The additional low adhesive sheet is therefore pulled by and peeled off gradually and progressively in a direction to the upstream edge from the downstream edge of the cooled portion when the layers of plastic film are fed again after being cooled.